The traditional architecture of a telecommunications network comprises a central office, remote terminals, and subscribers' equipment. Typically, the central office sends multiplexed electrical signals to the remote terminals which demultiplex the signals and send particular signals to devices of particular subscribers.
Recently, new architectures, optical networks, have been developed. Such networks are typically comprised of a central office, active remote nodes, optical network units, and subscribers' equipment. In this new architecture, waveguides, such as optical fibers, are used to connect central offices with remote nodes, and remote nodes with optical network units ("ONUs"). Optical signals from the central office are converted to electrical form, switched, converted back to optical form and sent to the ONUs. The use of optical fibers and the demand for more channels and higher capacity are increasing the projected throughput and complexity of telecommunications networks and the cost of remote receivers, transmitters, switches, and processors.
Passive Optical Networks ("PONs") have been proposed to alleviate these problems. In PONs, connections between the central office and the remote nodes, and connections between the remote nodes and the ONUs are made through optical fibers, eliminating the optical to electrical and electrical to optical conversions. Optical signals are sent from the central office and split into portions. Each portion is then sent to a particular ONU. The ONUs convert the optical signals to electrical signals and send the electrical signals to one or more subscribers' devices.
One current PON architecture is the broadcast PON, in which a common set of data signals is sent to all ONUs. However, in this architecture a particular ONU's data is sent to every other ONU, which wastes power and restricts the bandwidth capacity of the network. In addition, these networks are not secure because unauthorized ONU transmissions can corrupt the remote nodes.
Another known optical network architecture uses wavelength division multiplexing ("WDM") and demultiplexing of optical signals at remote nodes. To connect the central office to an ONU, the central office must transmit at the correct wavelength. WDM causes each optical signal to be directed to a single ONU and thus overcomes problems associated with broadcast PONs. Some WDM systems employ Remote Interrogation of Terminal Equipment ("RITE-Net"), a technique in which a portion of the downstream optical signal from the remote node is modulated by the ONU and returned to the remote node as the upstream optical signal. Cost and technological immaturity have kept WDM optical networks, and in particular WDM RITE-Net optical networks, from being implemented. A WDM RITE-Net technique is disclosed in a pending application to Darcie et al., Ser. No. 08/029,724, filed Mar. 11, 1993. The contents of that application are incorporated by reference herein.